We investigate the local integrability of a family of three dimensional quadratic systems in a neighborhood of (0:|1:1)(0:|1:1) resonant singular point. We find the necessary and sufficient conditions for the existence of two functionally independent first integrals of the system. Mechanisms for integrability for the systems are either time-reversibility or Darboux integrability.
COBISS.SI-ID: 20150536
Since Chicone and Jacobs investigated local bifurcation of critical periods for quadratic systems and Newtonian systems in 1989, great attention has been paid to some particular forms of cubic systems having special practical significance but less difficulties in computation. This paper is devoted to the linearizability and local bifurcation of critical periods for a cubic Kolmogorov system. We use the Darboux method to give explicit linearizing transformations for isochronous centers. Investigating the finite generation for the ideal of all period constants, which are of the polynomial form in six parameters, we prove that at most two critical periods can be bifurcated from the interior equilibrium if it is an isochronous center. Moreover, we prove that the maximum number of critical periods is reachable.
COBISS.SI-ID: 19614984
We study the universal nature of the product of the entropies of all horizons of charged rotating black holes. We argue, by examining further explicit examples, that when the maximum number of rotations and/or charges are turned on, the entropy product is expressed in terms of angular momentum and/or charges only, which are quantized. (In the case of gauged supergravities, the entropy product depends on the gauge-coupling constant also.) In two-derivative gravities, the notion of the "maximum number" of charges can be defined as being sufficiently many nonzero charges that the Reissner-Nordstrom black hole arises under an appropriate specialization of the charges. (The definition can be relaxed somewhat in charged anti-de Sitter black holes in D )= 6.) In higher-derivative gravity, we use the charged rotating black hole in Weyl-Maxwell gravity as an example for which the entropy product is still quantized, but it is expressed in terms of the angular momentum only, with no dependence on the charge. This suggests that the notion of maximum charges in higher-derivative gravities requires further understanding.
COBISS.SI-ID: 77565697
The purpose of this note is to extend the results obtained in [1] in two ways. First, the six-dimensional F-theory compactifications with U(1) x U(1) gauge symmetry on elliptic Calabi-Yau threefolds, constructed as a hypersurface in dP(2) fibered over the base B = P-2 [1], are generalized to Calabi-Yau threefolds elliptically fibered over an arbitrary two-dimensional base B. While the representations of the matter hypermultiplets remain unchanged, their multiplicities are calculated for an arbitrary B. Second, for a specific non-generic subset of such Calabi-Yau threefolds we engineer SU(5) x U(1) x U(1) gauge symmetry. We summarize the hypermultiplet matter representations, which remain the same as for the choice of the base B = P-2 [2], and determine their multiplicities for an arbitrary B. We also verify that the obtained spectra cancel anomalies both for U(1) x U(1) and SU(5) x U(1) x U(1)
COBISS.SI-ID: 77563649
We study the 1D Hamiltonian systems and their statistical behaviour, assuming the initial microcanonical distribution and describing its change under a parametric kick, which by definition means a discontinuous jump of a control parameter of the system. Following a previous work by Papamikos and Robnik (J. Phys. A: Math. Theor. {\bf 44} (2011) 315102) we specifically analyze the change of the adiabatic invariant (the action) of the system under a parametric kick: A conjecture has been put forward that the change of the action at the mean energy always increases, which means, for the given statistical ensemble, that the Gibbs entropy in the mean increases. By means of a detailed analysis of a great number of case studies we show that the conjecture largely is satisfied, except if either the potential is not smooth enough, or if the energy is too close to a stationary point of the potential (separatrix in the phase space). Very fast changes in a time dependent system quite generally can be well described by such a picture and by the approximation of a parametric kick, if the change of the parameter is sufficiently fast and takes place on the time scale of less than one oscillation period. We discuss our work in the context of the statistical mechanics in the sense of Gibbs.